This invention relates to the manipulation of electrical cable, and more particularly to the winding and unwinding of highly sensitive instrumentation cable by a drum or reel.
In a variety of fields of use, high quality electrical cables carry information which must not be measurably degraded by the cable itself. For example, in connection with the inspection of manufactured components or operating equipment, where strain gages, eddy current, or ultrasonic probes are often used, and in sound reproduction systems, the signal characteristic must be preserved. This poses a problem when the signal source is remote from and moveable relative to, the signal processing equipment. The feeding out and retrieval of the cable during signal transmission must not introduce high frequency noise, which can spoil the signal.
As a more specific example, in connection with the inspection of tubes in the steam generators of nuclear power plants, the inspection probe must be remotely driven up into each tube at a controlled rate of advance, and the probe position at any moment must be known exactly, so that the ultrasonic output signal can be correlated with a unique location in the tube. This is often accomplished using a precisely grooved and dimensioned drum to withdraw or advance the cable.
One major problem associated with drum drives is the deleterious effect on the cable of the torsion resulting from the rotation of the drum. Typically, one end of the cable is connected to a fixed member, such as plug or socket. Because of the high frequency noise they generate, slip rings between the cable and drum cannot be used. As a result, continual torsional stresses cause rapid degradation of the cable used in such inspections, necessitating a frequent replacement. Since steam generator inspection is often on the critical path of work to be done during nuclear power plant outages, a significant benefit can be achieved by providing a torsionless cable connection for the drum.